<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script type="text/javascript" src="http://www.masaikk.xyz/jquery-3.5.1.min.js"></script>
    <script>
        function f1() {
            $.post(
                'http://localhost:8090/lg',
                {mess:'from ajax'},
                (data)=>{
                    alert(data);
                }
            )
        }
    </script>
</head>
<body>
<div>
    <button onclick="f1()">sendAjax</button>
</div>

</body>
</html>